The present invention relates to a digital transmitter and a method for calibrating a digital transmitter, and more particularly to a low noise and low cost digital transmitter and related calibration method.
In wireless communication system, using a digital transmitter to digitally amplify and transmit RF (Radio Frequency) signal can be the most area saving and power efficient way. Conventionally, there have two ways to implement the digital transmitter. The first type is thermo-coding, and the second type is binary-coding. For the thermo-coding digital transmitter, the output power is a combination of a plurality of unit powers outputted by a plurality of unit cells. Therefore, a thermo-coding digital transmitter may need a lots of unit cells to generate a high power output signal. On the other hand, the binary-coding digital transmitter uses a plurality of binary-coding cells to generate an amplified output signal. The number of the binary-coding cells is less than the number of unit cells of the thermo-coding digital transmitter because the binary-coding cell may generate power higher than the unit power of the thermo-coding digital transmitter. However, the coding cells may have different cell delays. The different cell delays of the coding cells may increase the noise floor of the amplified output signal because the coding cells may output their respective signals at different time.
Therefore, how to solve the cell delay problem of a digital transmitter is an urgent problem in the field of wireless communication system.